Lanthanum manganite, modified by substitution of calcium or strontium ions for part of the lanthanum, is used as an electrode material for high temperature solid electrolyte fuel cells. Lanthanum chromite, also modified by substitution of calcium or strontium ions for part of the lanthanum, has been considered for use as an air electrode, or as both an air electrode and a support material for high temperature solid electrolyte fuel cells. These fuel cells are made of successive layers of bonded ceramic materials which perform the functions of support, air electrode, electrolyte, fuel electrode, interconnection, and other functions. In order that the fuel cells remain undamaged during thermal cycling between the high temperatures of fabrication or operation, and room temperature, it is desirable to match the thermal expansion characteristics of the various layers that make up the fuel cells. If the various layers are mismatched in thermal expansion characteristics, the layers can crack during thermal cycling and render the fuel cell ineffective or at least less effective.
A difficulty in constructing the fuel cells using the modified lanthanum manganite and modified lanthanum chromite is that these materials, modified to have the highest electrical conductivity, have a higher coefficient of thermal expansion than do some other materials typically used in making the fuel cell, such as those used in the stabilized zirconia electrolyte or the stabilized zirconia support tube. While the coefficients of thermal expansion of the various materials depend on the exact composition selected for a particular fuel cell, it would be highly desirable to be able to adjust the coefficients of thermal expansion of lanthanum manganite and lanthanum chromite to match the coefficients of thermal expansion of the other materials. In this way, these materials could be used in fuel cells without cracking of any of the cell components during thermal cycling.